1. Field of the Invention
The present invention relates to a system for controlling a combustion engine and an automatic transmission and, more particularly, to a system for controlling a combustion engine and an automatic transmission so adapted as to ease a shift shock which may be caused upon starting the operation of shifting the automatic transmission mounted to the automotive vehicle.
2. Description of Related Art
Among automatic transmissions mounted to the automotive vehicles, there have been extensively employed those in combination of a torque converter consisting of a pump impeller, a turbine runner and a stator with a transmission mechanism of a multistage gear type to be connected to the turbine runner of the torque converter. To the automatic transmission is usually mounted a control system of hydraulic pressure circuit type which is so arranged as to shift the states of coupling friction coupling elements such as clutches and brakes in the shift mechanism, thereby performing shift operation.
It is to be noted that, when the shift operation is performed by the automatic transmission, the vehicle speed little changes due to inertia of the automotive vehicle while the number of revolutions of the input shaft changes rapidly in accordance with a gear ratio of the automatic transmission, thereby causing a rapid variation in torque of the output shaft of the automatic transmission. And the acceleration of the automotive vehicle body rapidly changes due to such a rapid variation in the torque of the output shaft of the automatic transmission. In other words, a so-called shift shock may be caused. One of measures to ease such a shift shock is to control the operating oil pressure to be supplied to friction coupling elements in the shift mechanism so as to smoothly couple or uncouple the friction coupling elements. This measures may raise the problem that, when attempts have been made to thoroughly suppress this shift shock, the friction coupling elements are kept for a considerably long period of time in a freely sliding state so that the friction coupling elements may be reduced or abraded rapidly.
Another technology is disclosed in Japanese Patent Laid-open Publication (kokai) No. 97,350/1984, which involves changing output of the combustion engine in synchronization with the shift operation of the automatic transmission, thereby easing the shift shock.
It is to be noted herein that, for the technology involving changing the output of the combustion engine in synchronization with the shift operation of the automatic transmission, it is necessary to accurately detect the point of starting and ending up the shift operation. In other words, as shown in FIG. 5, a peak as indicated by reference symbol "A" appears as protruding on the torque of the automatic transmission, in accompany with the start of the shift operation, when the reduction of the output of the combustion engine is delayed from the start of the shift operation. This protrusion of the torque of the automatic transmission may cause a so-called shift shock. Further, when the output of the combustion engine is returned prior to the end of the shift operation, the torque of the output shaft of the automatic transmission appears protruding as indicated by reference symbol "B" and this protrusion may cause a shift shock, too. It is also to be noted herein that it is actually difficult to directly detect the points of starting and ending up the shift operation, i.e. the states of coupling the friction coupling elements for performing the shift operation of the multi-stage shift mechanism. Hence, it is necessary to indirectly detect the points at which the shift operation of the automatic transmission has been started and ended.
The previous patent publication discloses the technique of indirectly detecting the points of starting and ending up the shift operation on the basis of a variation in a change ratio of the number of revolutions of the combustion engine. This technique can be said effective particularly when changes in the number of revolutions of the combustion engine can remarkably be recognized, i.e. when a peak can appear for the number of revolutions of the combustion engine, as in the case where the automatic transmission is upshifted during the course of acceleration. However, it is to be noted that the mode of driving during shift operation may be so irregular and diversified that a peak for the number of revolutions of the combustion engine does not always appear at the time of starting the shift operation. Hence, the aforesaid technique suffers from the difficulty of setting a threshold value. If the threshold value would be set too small, on the one hand, then a slight change in the number of revolutions of the combustion engine might be determined as the point of starting the shift operation or ending up the shift operation, thereby causing the risk of making too early determination. If the threshold value would be set too large, on the other hand, then the start and the end of the shift operation can be determined for the first time at the point when the number of revolutions of the combustion engine have changed largely so that the determination may be made too late.